Crew willing to do unplanned spacewalk on array
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 15, 2006
Flight controllers tried additional "wiggle" tests late today to shake a hung-up guide wire loose and clear the way for full retraction of a partially folded solar array. As with earlier tests, results were inconclusive but the Discovery astronauts said they would be willing to stage a repair spacewalk if mission managers conclude a quick repair is necessary and can be safely carried out.
"We have a great view of what's going on with the array up there from the shuttle flight deck," said station commander Mike Lopez-Alegria. "My perspective looking at it from the inside last time was it doesn't need much coaxing. You've probably heard us use the analogy of trying to fold a map. As you know, at times when you're folding a map it's helpful to poke it here and there. I think our approach will be not very different from that, although we'll be poking gently."
NASA's Mission Management Team met today to discuss a variety of options to fully retract the P6-4B solar array wing. The wing currently is retracted a little more than half way with at least one guide wire hung up on a grommet that seems to be preventing the slats in a solar blanket from folding smoothly.
Earlier today and again late this afternoon, flight controllers sent commands to move the array's mast slightly to trigger a wave-like motion in the folding slats that make up the solar blanket. The idea was to set up enough motion to free the guide wire from the friction believed snagging it in a grommet.
Television views from space showed the blankets rippling gently, but it was not immediately apparent whether the gentle shaking accomplished anything.
It appears unlikely NASA managers will add any solar array tasks to an already-planned spacewalk Saturday to finish a major re-wiring job to switch the international space station's circuitry form an interim to a permanent power system. The station's robot arm likely would be needed on the left side of the complex to provide access to the base of the array and the arm is needed on the right side of the station to support Saturday's spacewalk. But as of this writing, no options have been ruled out.
If a spacewalk is added to the mission, either Sunday or Monday, the Discovery astronauts would have to give up a planned post-undocking heat shield inspection. Commander Mark Polansky told reporters today he would be willing to do that if managers decide retracting the array is the higher priority.
"Certainly we rely a lot on the imagery team on the ground to go ahead and take a look and tell us that they think everything is going well with the orbiter, which we've gotten so far," he said. "There are a lot of risk trades here and we have a mission to accomplish. So I'm sure (we will) take a look at risk versus reward and see what's the best thing to accomplish.
"In a perfect world, I'd like to have everything but it's not quite that perfect. So we'll go ahead and try to find out what's the best thing we could do for overall mission success and safety."
Saturday's re-wiring spacewalk will be carried out by Robert Curbeam and newly arrived station astronaut Sunita Williams. But a solar array repair job would be carried out by Curbeam and Christer Fuglesang, who trained for solar array contingencies before launch.
Working around the array carries some risk because of sharp edges, minimal training and the possibility of arcing that could lead to potentially dangerous electric shocks. But any tools would be insulated and Curbeam said he was not particularly worried.
"I"m really not concerned at all about the shock hazard," he said. "We've got a great team on the ground working on a plan and hopefully it'll work well for us. But if nothing else, I know it will be safe for us so I'm not concerned about the shock hazard at all.
"Of course, we're excited about the possibility of helping out and helping make the house up here a little bit better by fixing that solar array if we can."
NASA managers also are considering deferring any additional work to the next shuttle mission or to the station's crew after Discovery departs. If an unplanned spacewalk is added to Discovery's mission, a decision must be made soon.
"The biggest thing about it is there's a lot of very delicate pieces to the solar array wing and we want to make sure we don't rip one of those blankets or damage any of the hardware that's up there," Curbeam said. "As always, you want to do no harm first."